Radiation is used to treat cancer and other diseases of the body. Radiation has long been proven to destroy fast multiplying cells (e.g., cancer) in hopes of destroying or preventing the spread of the disease. Brachytherapy, which is the treatment of cancer at close distances, is one example of the use of radiation for treating diseases of the body. During brachytherapy, a radioactive source or sources are positioned in the area needing treatment. Depending on the shape, size and delivery means of the radioactive sources, the sources are either kept permanently in the body or removed after a specific amount of time. Since permanent implants are tiny seeds approximately 3 mm long and 0.5 mm wide, the use of these seeds do not relate to the present invention. Consequently, the focus of this application will be on the field of temporary implants.
The term temporary implants describes the procedure of maneuvering a radioactive source or sources to the treatment site utilizing a transport catheter or tube which has been previously placed in the vicinity of this treatment site. Alternatively, the transport catheter and temporary implant can simultaneously be maneuvered to the treatment site. In either situation, after a specified period of time, these sources and the transport catheter or tube are removed from the body. Since the radioactive source or sources may encounter a tortuous path in various arteries, veins, ducts, or the like inside the body to reach the treatment site, the radioactive source is usually attached by some device to a flexible drive member. This source and the drive member may be used many times, and, therefore must be able to withstand the many bends it encounters when it is maneuvered to the treatment site or removed therefrom, without breaking.
There are several devices on the market in which radioactive sources are attached to flexible drive members. Each of these devices is constructed in a different fashion and each has its limitations. Examples of these prior art devices are described in U.S. Pat. Nos. 4,819,618 and 5,141,487, both issued to Liprie as well as U.S. Pat. No. 4,861,520 issued to van't Hooft. The two Liprie patents describe a radioactive element which is attached to a drive member by means of a junction welded to the drive cable. The patent to van't Hooft describes an apparatus which attaches radioactive sources to a drive cable by means of a stiff capsule welded into the end of the cable. Since the most resistive portion to flection of any flexible material, such as a cable, tube, or wire is the segment closest to the end, to join a capsule which is stiffer than this material and welded onto its end would only add to the resistance to bending and would adversely effect maneuvering the material through the body.
U.S. Pat. No. 5,084,002 issued to Liprie describes an ultra-thin high dose iridium source included within an oversized hole drilled inside the end of a solid platinum wire. Drilling a hole into a thin wire is very difficult since the maximum depth the hole can be drilled is equal to approximately seven times the outside diameter of the wire. To drill a hole deeper than this is extremely difficult due to the drifting of the drill as it burrows the hole. This drifting can lead to a thinning of the cavity walls which greatly increases the chances of breakage. This breakage is often disastrous, resulting in unwarranted radiation exposure. A larger outside diameter wire will be needed to compensate for the drifting and still allow the walls of the cavity to be thick enough to withstand stress. Unfortunately, this larger diameter wire might be too large to fit into many constricted areas of the body. As described in Liprie '002 one can drill a cavity inside a solid wire, if one starts with an oversize wire and an oversize hole and then the whole assembly is drawn down to the desire diameter of the wire. However, whenever a wire is drawn down, the assembly containing the cavity elongates and the precise positioning of the radioactive core inside the assembly can become very difficult. Additionally, this larger diameter wire would result in less flexibility and may not be able to be maneuvered to the treatment site.
Finally, U.S. Pat. No. 5,282,781 issued to Liprie employs tube, a backbone wire, a pure iridium core and a plug and draws down the entire assembly to form a tight seal between the housing material and the backbone wire and the plug. Without this drawing down of the housing onto the backbone wire, radioactive flakes from the core would migrate throughout the inside of the assembly wire, resulting in unwanted contamination. This "drawing down" step would increase the costs and difficulty of manufacturing the source wire. Furthermore, any "drawing down" step as described in U.S. Pat. No. 5,084,002 and U.S. Pat. No. 5,282,781 would not work on a memory resistant alloy. As soon as a memory resistant alloy had been drawn through a die, the alloy would resume its original shape. If the memory resistant alloy was drawn beyond the threshold of its elasticity, then the memory resistant properties of the alloy would be destroyed.
Thus, there exists a need for a radioactive source wire that has an extremely small diameter and is flexible, yet has sufficient tensile strength to traverse a tortuous route of bends and turns without breaking.
It is an object of the present invention to provide a small diameter source wire that is extremely flexible and will allow the source to travel to the site of treatment without binding.
It is another object of the present invention to provide a source wire that is strong enough to withstand the stresses placed upon the source, as it is maneuvered to and from the site of treatment within the patient, without breaking.
Yet another object of the present invention is to provide an improved source wire design that includes a mechanism for relieving some of the stress encountered by the metal housing tube of the source wire as it is maneuvered to the treatment site.
Still yet another object of the present invention is to provide an improved source wire that exhibits little or no memory retention when bent.
An additional object of the present invention is to provide for improved methods of manufacturing source wires that would decrease the costs and difficulty in manufacturing source wires without sacrificing the quality of the manufactured source wire.